1. Field of the Invention
The present invention relates to a hybrid integrated circuit device, more specifically, to a hybrid integrated circuit device having a semiconductor element which operates at a high frequency.
2. Description of the Related Art
A configuration of a conventional hybrid integrated circuit device 100 will be described with reference to FIGS. 6A and 6B. FIG. 6A is a plan view of the conventional hybrid integrated circuit device 100 and FIG. 6B is a cross-sectional view thereof.
Referring to FIG. 6A, a conductive pattern 102 is formed on a surface of a metal substrate 101, which is made of metal such as aluminum, through an insulating layer 107. A desired hybrid integrated circuit is realized by mounting a circuit element 105 in a predetermined position of the conductive pattern 102. Here, an integrated circuit chip (IC), a chip resistor, a chip capacitor, a power transistor or the like is adopted as the circuit element 105, and a transistor which is mounted face up is electrically connected to the conductive pattern 102 through a fine metal wire 103. A plurality of pads 102A made of the conductive pattern 102 are formed on one side edge of the metal substrate 101, and leads 104 are fixed to these positions with a brazing material such as solder. One of applications of the hybrid integrated circuit device 100 configured as described above includes an audio amplifier module, for example.
In addition, to avoid occurrence of parasitic capacitance between the metal substrate 101 and the conductive pattern 102, a lead 104A connected to ground potential is electrically connected to the metal substrate 101 through the conductive pattern 102 and a contact portion 108. Moreover, the hybrid integrated circuit device 100 having the above-described configuration is sealed with a casing material or sealing resin.
However, the above-described hybrid integrated circuit device has the following problems.
Specifically, when a D-class amplifier circuit configured to operate at high speed is formed on the surface of the metal substrate 101, electric potential of the metal substrate 101 is changed by a capacitance which is generated between the conductive pattern 102 and the metal substrate 101. Such a change in electric potential adversely affects electric signals which pass through other parts of the conductive pattern 102, and resultantly causes noises in an audio output.
Moreover, an inductance component is generated in the lead 104A which is connected to the metal substrate 101. Such an inductance component destabilizes operations of the entire device. On the other hand, if the metal substrate 101 is set electrically independent in order to avoid this problem, it is not possible to suppress unnecessary radiation.